(1) Field of the Invention
The present invention relates to a stabilizer composition for a chlorine-containing polymer and a process for the preparation thereof. More particularly, the present invention relates to an inorganic stabilizer composition comprising a zeolite as a main stabilizer component and a process for the preparation thereof.
(2) Description of the Related Art
When a chlorine-containing polymer, for example, a vinyl chloride resin, is exposed to light, dehydrochlorination is caused in the molecule chain, and decomposition and discoloration are caused. Various stabilizers and stabilizer compositions have been proposed and widely used for stabilizing vinyl chloride resins against this thermal decomposition.
Japanese Examined Patent Publication No. 58-18939 teaches that an aluminosilicate of a type A zeolite structure having a predetermined ion exchange capacity is incorporated as a heat stabilizer in a chorine-containing polymer.
Japanese Unexamined Patent Publication No. 61-34042 teaches that a zinc salt of an organic acid and a metal salt of a halogen oxyacid are incorporated together with an aluminosilicate of a zeolite crystal structure into a halogen-containing resin.
A zeolite type stabilizer is advantageous in that the stabilizer can be easily incorporated in a chlorine-containing polymer and bleeding is not caused in the resulting composition, and the stabilizer is cheap. However, at the initial stage after the incorporation, the chlorine-containing polymer tends to be discolored to some extent, and under ordinary application conditions, the heat stabilizing effect is still insufficient.
Accordingly, a zeolite type stabilizer is not used as a main stabilizer component of a stabilizer composition for a chlorine-containing polymer, though it is commercially used as a subsidiary stabilizer component.
It is considered that the reason why the zeolite is still insufficient for the heat stabilization of a chlorine-containing polymer is that the content of a metal component effective for capturing chlorine is not sufficiently high. Furthermore, it is considered that occurrence of discoloration at the initial stage after the incorporation is due to the presence of the above-mentioned metal component, as in case of other inorganic stabilizers. Accordingly, in case of zeolite type stabilizers, as in case of other inorganic stabilizers, it is difficult to simultaneously attain a sufficient heat stabilizing effect and an effect of preventing discoloration at the initial stage.